Variable position control for hydraulic servomotors



Oct 1952 E. H. FLETCHER ETAL 2,615,430

VARIABLE POSITION CONTROL FOR HYDRAULIC SERVOMOTORS- Filed May 19, L951 a Sheets-Sheet 1 I N V EN TORJ' E li F/eic/zei', BL. Hanson &

' BY Nab v a Aiiorngs O 1952' E. H. FLETCHER E'TAL 2,615,430

VARIABLE POSITION CONTROL FOR HYDRAULIC SERVOMOTORS Filed May 19, 1951 3 Sheets-Sheet 2 INVENTORS EJZF/efcberJFLHonson 8r T. Nakae transport and ground-working positions.

Patented Oct. 28, 195 2 VARIABLE POSITION CONTROL FOR HYDRAULIC SERVOMOTORS Edward H. Fletcher, Cedar Falls, and Paul L.

Hanson and Takuro Nakae, Waterloo, Iowa, assignors to Deere Manufacturing 00., Dubuque, Iowa, a corporation of Iowa Application May 19, 1951, Serial No. 227,246

This invention relates to a hydraulic system and more particularly to means for controlling .the extent of relative movement of hydraulically powered parts. 1

The embodiment of the invention disclosed herein was designed primarily for and finds its greatest utility, inconnection with the control of adjustable parts of agricultural implements. In the ordinary situation, an agricultural implement, such as a plow, is drawn by a tractor and has a plow bottom adjustable vertically between The tractor is equippedwith a hydraulic pump and distributing valve that form part of a fluid-pressure system including a fluid motor for adjusting the plow. This motor ordinarily takes the form of a cylinder and piston assembly, one end of the cylinder being anchored on the plow frame and the free end of the piston rod being connected to appropriate linkage for raising and lowering the plow.

In the operation of a tractor-plow unit of the type described generally above, it is necessary for the operator-to actuate the fluid-pressure system at the end of each furrow to eifect raising of the plow bottom .from its ground-working position, so that the unit can be turned. about and driven over the field to. cut an adjacent and parallel furrow. It is desirable in instances such as these that means be provided to enable the operator to lower the plow bottom again to the same groundworking position as before. In the fluid-pressure systems known .in, the past, it has been customary to provide a stopcooperative between the cylinder and the piston .to positively determine the extent of relative movement between the two, and consequently to determine the extent of lowering of the plow bottom to ground-working position.

Although stop means such as this is generally satisfactory, it isf'found in some circumstances that it is desirable or necessary to lower the plow bottom to an extent greater than its previous 7 working depth. If the stop means is rigidly al- 7 Claims. (Cl. 121-38) to or from the chamber of the fluid-pressure cylinder, so that when the system reaches a predetermined point in its stroke, the valve is partially closed to an extent sufficient to permit throttling action which so restricts the passage as to create an abnormal rise in pressure, with the resultvthat the safety or pressure-relief valve of the system is caused to operate, whereupon the distributing valve control lever is returned to neutral and fluid pressure is no longer transmitted to the cylinder. Inasmuch as the closing action of the valve is not positive; that is, the valve does not completely close the passage, there is a restricted passage through which fluid may flow at areduced rate. Therefore, the operator can again move his control valve to operating position and thus allow the system to circulate fluid at such reduced rate, thereby allowing further relative movement between the cylinder and piston in the same direction but at a lower speed.

A further object of the invention isto incorporate in the valve means for completely or positively closing the passage after a predetermined extent of relatively low-speed movement between the cylinder and piston so that after-such predetermined amount of travel, a positive stop be.- tween the cylinder and piston is efiected.

The invention has for a further feature the provision of improved valve means of the-character specified which is so constructed and designed as to require a minimum of modification in by:- draulic systems of existing types.

Other objects and important features inherent in and encompassed by the invention will become apparent to those versedin the art as a complete disclosure of a preferred embodiment of themvention is made in the followin detailed descriptionand accompanying sheets of drawings, in which Y Figure 1 is a partial side elevational view of a tractor and attached plow equipped with a hydraulic system having the components as outlined above;

Figure 2 is an enlarged sectional view of one type of distributing valve for the hydraulicrsystem; 1' Figure 3 is anenlarged top planview lofithe cylinder and piston assembly, with aportion of the cylinder being broken away to disclose one of the fluid passages therein;

' Figure 4 is a longitudinal sectional view taken substantially'on the 11ne14 4 ofFigure-3, showing'the piston in its-fullyextended position:

Figures 5 and 6 are 'longitudinal'sectional views similar to Figure 4 but showing the piston indif- 3 ferent positions and likewise showing difierent positions of the components of the control means;

Figures '7 and 8 are end and side elevational views respectively of one of the detail parts of one form of adjustable stop means;

Figures'Q and '10 are side and'endelevational views of a modified form of stop means.

Hydraulic system in generaL-Figures 1 and 2 As mentioned above, the embodiment of the invention disclosed herein was designed primarily for use with an agricultural unit of the type ineluding a power vehicle and an implement having an adjustable part. It will be understood, of course, that the invention has wider application. Further, the specific illustration of tractor and attached plow is merely representative of one of the several applications of which the invention is capable. Therefore, the present disclosure should be taken as illustrative and not limiting.

' The tractor illustrated in Figure 1 is typical of a conventional tractor and has a longitudinal body 2'0 carried on right-land left-hand traction wheels 22 and'M, a portion of the left-hand wheel being broken away to exposea distributing-valve housing 28 which contains a distributing valve (Fig. 2 that forms part of a hydraulic or. equiv.- lent fluid-pressure system. The distributing valve is operated by a control lever 28 that is con venientto an operators seat 30 on the tractor.

Referring now to figure '2, it will be seen that the distributing valve comprises a casing having a high 'pressure -or inlet passage 32 that is suppl-ie'd with fluid under pressure by means of a circulating pump 35. This pump has an intake 36 connected to :a reservoir 38. The reservoir in turn communicates through a line ii! with a lowpress'ure passage 42 in the distributing valve housing or casing 26. I

The distributing valve casing is provided wit a vertical valve bore 3:? within which is carried a shi'ftable valve '46. This bore communicates intermedi'ate its ends with the high-pressure passage 32 and the valve i6 is operative to "e'ilectcontrol of a pair of motor ports 48 and 50 and a pair of exhaust ports 52 and '8. The motor ports 48 and 50 are provided respectively with "springloaded check valves 55 and 58. The exhaust ports 52 and 54 are respectively connected by branch passages Gil-and 62 with the low-pressure passage '42.

.The valve 46 is s'hiftable selectively in opposite directions vertically in thevalve bore 44 by means of 1in=kage64 connected to an arm 63 fixed to a :ockshaft I58. This-rockshaft extends at one side 3f the distributing valve and is fixed to the lower and of the control lever 28. The upper motor tort 48 is connected -by a fluid-press1.1're-transmitling means including a hose T8 to one end of a fluid-pressure motor designated generally by the numeral "I2. The lower motor port 59 is similarly connected by a hose M to themotor I2. .The motor has first and second members, hererespectively in the form of a cylinder i6 and piston 7 8 (Figures '4, 5 and '6). The interior of the cylinder member is provided as a chamber to which'fiuid maybe supplied or from which fluid may be ex- "hausted to-effect "back-and-forth movement of "the piston 1-8. The member comprising the piston I8 further includes an external part in the form of a piston rod 88; the ireeor outer end of which has a clevis 82 for effecting connection to a rockable arm 84 pivoted at 86 one. plow frame 88. The closed end of the cylinder I6 has a clevis 90 anchored to the plow frame 88.

. raise the plow frame 32 and plow I88 relative to the ground-engaging wheel 98. Substantially full extension of the piston rod 89 is illustrated in Figure 1.

Conversely, retraction of the piston rod 88 will effect counterclockwise roekin of the bell crank selected operation of the system, fluid is exhausted from the left-hand end of the cylinder I6 via the lower hose I4 and ultimately through the branch passage 62, low-pressure passage 42 and line til/to thereservoir 38. When the fluid-pressure flowis reversed, fluid under pressure is supplied through the lower hose i l to the left-hand'end cf the cylinder it for efiecting extension of the pistonrod and consequently raising of'the plow bottom I80.

At the same time, the upper hose 16 becomes a medium for transmitting fluid exhausted from the right-hand end of the cylinder back through the distributing valve casing to the reservoir 38. The connection of the plow'frame 88 to the tractor for travel of the two together is effected by a hitch including a drawbar 102 on the tractor and a draft member I04 on the plow, as is generally conventional.

The distributing valve illustrated is of the type in which the main control valve is automatically returned to neutral position upon the occurrence of an abnormal pressure rise in the system. The neutral position of the valve 46 is illustrated-in Figure 2. The rockshaft 68 has fixed thereto a centrally notched plate I06 which has its central or neutral position established by aespring-loaded arm and roller means I08. .The rockshaft 68 has als fixed 'theretoa radially extending plate I III having an arcuate edge II 2 formed about the axis of the rockshaft. The arcuate edge terminates at its'opposite ends in cut-off corners H4 and I IS. In the neutral or central position of the plate I I0 as illustrated in Figure 2, the arc'u-- ate edge H2 is engaged by a roller I I8 carried "on one arm I20 of a bell crank having a second arm I22. A rod I24 depends from the freeend of the bell crank arm I22 into a vertical bore I26 and is headed at I28 to confine one end-oi'a coiled compression springI-M, the other endof which is retainedby a radial wall .portionfl 32 .at the upper end of the bore I 26 I The bore I 2Bintersectsthelow-pressure passage 42 and is coaxial with. a second bore 434 which intersects the passage. 42 and-furtherintersects the high-pressure passage 32. The lower end of the bore I34 is provided with a valve seat I36 normally closed by a valve I38- biased to closed positionqbyga coiled compression spring M0,, The bore I34 is dividedinto upper :and lower portions by angi-ntermediate, apertured,

radial wall I42 above which iscarried a'valve' I44. This valve is headed at I46 and has an axial passage I48'opening at the lower end of the valve and a communicating radial passage I 50 opening belowthehead-I46.-

ln 'order that'loweringof the plow bottom I to ground-working position maybe effected, the control lever 28 is-moved rearwardly" from its position shown in Figure 1, thus effecting clockwise rocking- 0f the rockshait 68. 'Thisi's fob lowedby- 'downward movement ofthe valve '46. An enlarged intermediate portion I52 on the valve 46 cuts'ofl the lower portion of the valve bore-44 from communication with the high-pressure passage 32 and the upper motor port 48. --A lower tapered portion I54 on the valve46 simul'e taneously' efiects opening of the lower check valve 56. Exhaust fluid returning through the nose 14-and motor port 50 'may return to the reservoir via the exhaust port 54, the branch passage 62, the low-pressure passage 42 and linell. l

When the control lever 28 is moved forwardly to effect counterclockwise .rocking of the rockshaft 68, the valve 46 moves upwardly. in the valve bore,44,and, the valve portion I52 cuts off the upper portion of the valve bore so that fluid under-pressure is transmitted throughthe lower motor port 14 to the motor 12 Simultaneously, ange ed Portion at a 196 P rt n. 3 valve;4 6, opens the check valve 56 forthe motor port-.148. Exhaust fluid returning through the hose. 10,-and'mo-tor port 48 finds its. way to the reservoir through the exhaust port 52 ,the branch passage 60, low-pressure passage 42 and line '40.

; I l 1 e,main control valve 46 is maintainedin either its raise or lower position by means of the roller, II8 on the bell crank I20 I 22 an dis urged toward neutral position by the springloaded arm and roller I08. For example, when the rockshaf-t 68 is rocked in a clockwise direction to move the valve 46 downwardly; the notched plate I06 moves so that the end of the plate ratherthan the notchengages the roller onthfe arm and roller means I08. At the same time, the: arcuate edge II2 on the platel I0;;departs from the roller H8 and the cu-t-ofi corner II6;.e'ngages this;rol1er. The spring-loading ef fected by the compression spring I30-maintains the roller I I8 in engagement with thecut-off corner II6, and thus maintains the position of the main control valve 46. Now, should there occur an; abnormal rise in pressure in the system, -;the. relief valve I38 is unseatedand fluid flowing upwardly through the bore I34 raisesthe valve 144 to an extentsufiicient to-by-pass fluid pressure through thepassages I48 and 150 to the low-pressure passage 42 at the same time the head I46 of the valve I44 engages the headed end "I28 of the rod I24. This action moves the d aupwardly against the loading-of-the: spring I30. and-;releases engagement between the roller .I I8 and the cut-off corner II6 ontheplate H0.

The spring-loaded arm and roller means I08 is constantly urging the plate I06 (and consequently the rockshaft. 68.) to the intermediate or central position of Figure 2. Hence, the arm and rollermeans I08 is operative to return the rock- ;shaft andlhence the control va1ve 46 to neutral positiomwhereupon fluid may. circulate. idly be tween the pump and valve at :no appreciable pressu re.- 'Atwthe. same time, the two check valves 56 and58closejand maintain the position of the piston 18 relative-to thecylinder 16.

Fluid motw and control thereof-Figures 3 to 10 The cylinder or first motor member 16 has .an interior chamber I58 within which the piston 18 of thesecondmotor member is axially reciprocable and which is provided with appropriate passages for supplying fluid thereto or exhausting fluid therefrom at its opposite ends. 'Asbest showninf'Figure 3, the left-hand end for the cylinder 16 is'provided with first and second internally threaded openings I60 and I62." The passage of which the opening I60 forms apart includes an elongated cored passage portion I64 which runs lengthwise of the upper portion of the cylinder. This passage portion communicatesa't the right-hand end'of the cylinder with a genere allyannular groove I66 which is in part con'oen trio with the cylinder chamber I58. The coring of the passage portion I64 is facilitated by "the provision of. an opening I68 at the .right hand end of 'the cylinder. This opening is tapped and receives aclosure plug I10. H

Except for the communication at I66, the passage portion I64 is separated from the cylinder chamber I58 by an uppercylinder wall portion I12. "This wall portion is of substantial thick-'- ness and is'co-r'ed lengthwise thereof toprovide a. housing portionIM that opens at therighthand end-of the cylinder as a communicating lbore I16 and that opens at the left-hand end of the cylinder as a communicating bore I18 which in turn communicates through a reduced counterbore I80, with the opening I62 to which the hose 14 is connected. Theypassage portion'co'mprising the hore Ijincludes as "an extension thereof a further passage. portion I82 that conimunieates withthe leftrh-and end of the cylinder chamber I58 (Figures 4, 5 and, 6). Thebore portion I16 at the other end of the housing or chamber I14 is slightly enlargediat I 84 and is fitted with an appropriate annular jsea1 I 86 that is spring-loaded-at I88 and that is further provided with an axial bore I90. T The junction of the passage means I80'and 'I82 is efiected by a port I92, which port is here shown as including an annular seat. I if i The improved valve mechanism comprises a first or o'uter valve I94 of elongated construction carried for axial movement in the bore I18, and a second or inner valve 'I'96carried' for axial movement within an axial bore I88 that provides an interior in the first valve I94. 'I heleft-hand end of the valve I94 is'closed by a radialwall 200, with the exception of the provision of a throttling orifice 202. The radial wall 200 has an external seat 204 and an internal seat 206. The throttling rifice communicates with the interior of the valve I94 and combines with a second throttling'orifice 208 to constitute throttling passage means. communicating the seats 204 and 206. a

The axial bore I98 inthe' valve I 94gi'ves the valve an annular or circumferentia1 wall 210 that has on an external portion thereof an annular shoulder 2I 2 against which abuts one end of bias in means in the form of a coiled compression spring 2I=4. The other end of the spring abuts against a radial wall 2 I 6 forming partof the cylinder casting. Thus, the biasing means2'l4 norco tr ro 22 to he ri -ht valve seat 206 on the inside of the valve I94 to out out or close the throttling passage means 202 -208. The other end of the valve 196 is open. and is prox ma e to the o v en o he out "'valve I94. The valve I96 has a hollow interror provided by an 'axi-a1 bore 220. The lefthhnd'end of an elongated control member 222 received within the axial bore 220' and has a eaded term a tion 2 b h nd which i a outwardly opening recess provided by an annular sj i o e 225 e a nular wall p i e on the valve I95 becauseof the ax al bore 2 h s therei anon penin 228 i e i er wit the a nular groov h r c s 2.2.5.- A loc ing e t n he jorlmiof a small ball 230 is received in the opening 28 and recess 22.6 and p ve s ax al S arat f thie' a v 6 and ontrol m m er. 2 und r action of biasing means in the form of a light compr ss-ensur n 232511 s ring c beiwe n't e heade end 224 of t c t o rod and the interior of the valve I96. The annular wall 210 of the outer valve l 94 is extend d in such nanner as to Ol 'flrlie the ball 230; and as long as the parts are assembled, the annular wall 210 of thefvlalvev J94 prevents escape of the ball 230 the opening, thus establishing a connection between the valve I96 and control rod 222. The inn 'le sthof the r o e .2 nt al excoeds the maximum dimension of the :ball 23!]; therefore, the connection at 239-238 constitutes a lost-m conn c on. th p p ses of which wil pr se ly appe r- The control rod 222 extends outwardly through th bore 19!] in the seal [86 and has an external portion 234 on which is fixedly mounted a lug 236. 2

A control or stop element, designated generally by the numeral 238, is carried by the piston rod 81!. The disposition of the lug 23B is such that it ma be a me n a d y e top me s f lh is, .ast 'n s on o 0 an piston 8 more wargl the left, or in a direction in which fluid is ex.- hausted through the passage m ans tin-489 I62, the stop means 238 will engage the lug 238, thus'ishifting the control rod 222, to. the left and therefore the control rod reflects movement of t e p st andpis-ton rod ,8

The intermediate portion of the control rod 222 is provided witha pair of spaced-apart stops in the form of snap rings 2,40 and 242. Against one of these stops (24 0) and against the proximate open end of theouter valve 194 is a Washer 244 that abuts to the right against an annular slipulderflfi'formed in the bore J74. Bia'sing Q ans in the form of a coiled compression spring "248 acts between the washer 244 and the snap 242 and normally is operative to urge the "The form of stop ;m,eans shown in Figures 1 through '8 comprises a pair of plates 25%) and 252, each of which is circular as shown in Figure 7 and each of which has a central aperture 254.

j'lhe apertures are tolerablylarger than the piston rod 39 that there is a close sliding fit.

The description of this means in detail will be based on the plate 250, It will be understood, of coursathat the plates are identical but that they ar a symmetrically arranged in assembly. The plate 250 is out out at 25.6 and the cut-out portion is bent outwardly toprovide a lug 258.

{The other plate 252 has a similarlug 260. This lug appears only in Figure 3} When the two ,plates are assembled, the lugs 25;! and 260 are the two. plates are compres b y s c r d tceetht? by means of a ol 262 a d a wing nd lfifi- The b t ispassed th ou h. a pa r of a inni e tures :66 in the pl he as em 23.. ma be shifted axially on the piston red by loosening of the wing nut 264. When the assembly located in its d sire p ition it may be secu ed a ai st moveme t a i e to th 1 151 011 b tighten: ing the wing nut 264. n t at m o to means h in Eislirss 9 and 10, there is provided a plate 263 havin a split external th aded sl eve in the rm of a collet that embraces the piston rod .80. A sc ped nut 2 s t ead d on the s eeve 21!! a ma be loo en r t hten to clam the plate 268 adius b v to the iston od Bil f 1 In either case, the sto means may be soles; tivc y positioned o t e pis on od so that th poi t at which t u o t e c nt o od .222 is engaged may be varied. A shield or' shroud 214 may be provided for protecting the external portion 234 of the control rod 222 against accidental damage.

Qz mtidn When the fluid motor '12 is extended-that is; when the piston 18 is at the right-hand end-of the cylinder as shown in Figure ll-the stop means 238 will be spaced to the right from th'e lug 236 on the control or operating member 222. The operating member will be in its maininu n right-hand position because of action of the biasing means or spring 248, it being remembered that the spring or biasing means 2 holds the valve 194 also in its maximum right-hand 'posi tion and against the stop provided at 2444246. Now, when the maincontrol valve 46 is actuated to cause contraction of the motor {12, the piston 18 begins to move to the left, carrying with itithe piston rod 80, of course, and the stop mean s 238 i. Figure 4 may be taken as'representa tive of the instant just before the stop means 238 engages the lug 236 the stop means 238 continues its movement to the left along with the piston 18 and piston rod to, it engages the lug 236 and forces the 0011- trol rod 222' to the left. The spring 248is compressed between the stops established by the snap ring 242 and the washer 244 andthejrefore thespring 248 acts as force-transmitting means for forcibly moving the valve J94 to the left against the bias of the spring 2I4. This results, as shown in Figure 6, in movement of the valve 1i l4 to its port restrioting position, wherein the external seat 204 seats on the port seat I52 and wherein the throttling orifice 208 becomes alined with the passage 182; 'Iherefore, th only communication between the chamber I58 of the cylinder 1B and the passage l62--l80 l82 is viathe throttling orifices202 and 208.

The restriction set up by movement of the valve [.94 to its port-restricting position is sufli- 'cient to cause the mechanism of Figure2 to repiston 18 willmbve to-the left at a relatively slower speed, because of the restriction set up by agra ian the throttling orifices 202;;and208, Nevertheless, in-a situation such as this only slow speed will be desired. Inasmuch as the spring 248 can yield further between the StOpD Id valve I94 and the snap ring 242, the spring maybe said to constitute means accommodatingovertravel of the control member 222 beyond the stopped position of the valve I94. During this overtravel, the control rodx222 is effective to move the valve-I96 from the position shown in Figure to the, final position. shown inFigure 6.

;.During movement of the. valve I96,to its final position-by the control member 222 as the latter moves furtherto the left beyond the-position established by the stopped valve I94, the spring 232 acts as yieldable force-transmitting means between the headed end 224 of the control memher and the interior of the valve I96. As seen in Figure 6, the seat 2I8 of the valve I96 seats on the internal seat 206 of the valve I94 and thus cuts ..out or closes off the throttling means 2ll2.268, resulting in a second rise in pressure in' thesystem to actuate themechanism of Figure 2 for the purposetof returning the control valve 46 to its neutral position. The piston 18v is now at its, maximum left-hand position and there can be noovertravel. v I

In addition to the functions as previously 'described, the springs 248 and 232 have other im- 'portantfunctions. These followirom reversal of fluid pressure;-thatis,- the transmission of fluid pressure through the'hoseline I4 tothe left -hand end of the cylinder so that the piston can be moved to the I right. Fluid pressure against the closed end ofithe combined valve as- Y sembly forces the valve I96 -to the right against the spring 232 and forces the valve I94 to the right against the spring 248. This allows reversal of the piston at a relatively high speed, which would be unobtainable if initial fluid flow was forced to travelthrougha restricted passage.

'-'As the piston I8 and piston rod 88 move to the right, the stop means 238 is of course carried therewith. The springs 2M and 248 serve to restore the valve member I94 and control member 222 to their maximum right-hand positions for subsequent operation. Because of the inter connection at 23fl226-224, the inner or second valve I96 is carried along with the control member-222. I

; Because of the length of the annular groove or recess 2-26, the lost-motion means established by the ball or locking element 236 accommodates limited relative movement between the valve I96 and the control member, 'thus permitting the valve I96 to open upon the reversal of fluid pres, sure through the line I4. I

Summary The improved control valve mechanism for the hydraulic system provided according to the present invention achieves all the desirable results obtainable by mechanism heretofore known; that is, there is provided means for limiting the travel of ne motor member relative to another bythe The user of a system equipped with valve mechanism constructed according to the principles-of the present invention is thus able to achieve overtravel within a limited range,- which is of particular importance when the user knows precisely the-extent of overtravel that can be obtained. For example, in the present instance the amount of overtravel. available is one and one-half inches. Thus, the operator knows that his adjustment of an implement or equivalent part be yond the position he has preselected will not be excessive to the point of creating a dangerous e r-harmful condition. I

v Further objects and features of the invention not specifically enumerated above will undoubtedly occur to those versed in the art, as likewise willinumerous modifications and alterations in the preferred embodiment ofthe invention illustrated, all of which may be achieved without departingfrom the spirit and scope of the invention' as defined in the appended claims.

What is claimed is: j i

1. Ina fluid-pressure control system :having a first motormember formed with' a chamber and a passage including a port through which fluidmay flow incident to movement of a second motormember. within the chamberzzvalve means for controlling the flow of fluid out of the chamber for'sequentia'lly permitting, next restricting and finally: stopping such flow, comprising; a first valve movable back and forth. through a relatively short distance between a port-opening and a port-closing position, said first valve being elongated along its path'of movement andhaving an elongated hollow interior, said first'valve further having aport-proximate end including an outer seat formed with restrictive passage means and with an inner seat; first means biasing the first valve to its port-opening position; a second valve carried within the interior of the first valve for movement through a relatively longer dis tance between an open position and a closed position, said second valve having at one end thereof 'a closure element cooperative with the aforesaid inner seat to close the restrictive pas-' sage means in the first valve; a control member extending'loosely' lengthwise'into' the first valve and arranged to reflect movement of the second motor member in the direction that results in fluid flow out through the port; second means acting against the first valve and the control member and normally biasing the control member in the opposite direction; lost-motion means acting between the control member and the second valve for normally holding the second valve in its open position; said second biasing means serving also as yielding force-transmitting means between the control member and the first valve to move the first valve to its portrestricting position 'upon initial movement of the control member in the aforesaid. direction to a predetermined position, said second biasing means being yieldable to accommodate overtravel of the control member beyond said predetermined position; and said lost-motion means including a force-transmitting connection between the" control'member and second valve to effect closing of the second valve upon overtravel of the con trol member.

2. In a fluid-pressure control system-having a first motor member formed with a chamberanc a passage through which fluid may flow to eifec movement of a second motor member within-tbs chamber: valve means for controlling the new :i fluid for sequentially permitting, next restricting and an outer valve having an axial bore axially slidably receiving the inner valve and providing an annular wall surrounding the aforesaid opening and confining the lock element against radial escape from said opening.

7. Valve mechanism of the character described, comprising: an elongated control member having a cylindrical end portion provided with a terminal end and an outwardly facing annular groove closely behind said end; an inner valve having an axial bore therein receivin said end and providing an annular wall surrounding said end and said groove and arranging the valve and control member for relative axial movement, said annular wall having a radial opening therethrough in register with said groove; biasing '14 7 means within the valve bore and acting between the valve and said end of the control member to separate the two axially; a lock element in said opening and entering the groove to prevent such separation of the control member and valve; and an outer valve having an axial bore axially slidably receiving the inner valve and including an elongated portion overlying the aforesaid opening and confining the lock element against radial escape from said opening.

EDWARD H. FLETCHER. PAUL L. HANSON. TAKURO NAKAE.

No references cited. 

